A basic understanding of the components of chromosomes that are responsible for proper segregation, and the mechanisms by which these components are tied into the process of cell division, will likely result in unforseen medical applications to various genetic diseases, including some cancers. Toward this ultimate goal, a new model system is being developed for the study of centromeres which are more like those of vertebrates, but in an organism that is tractable for genetic and biochemical studies. The multicellular fungus Neurospora crassa, which has powerful genetic, molecular and biochemical tools, happens also to have centromeres that resemble those of higher organisms, both by cytological and molecular criteria. Recent cloning of a centromere from this organism into YACs will allow testing of these clones for activity as artificial chromosomes, either by transformation or by protoplast fusion of Neurospora. It should be possible to dissect function by use of a novel genetic assay that detects centromere function by creation of dicentric chromosomes in Neurospora. Concommitantly, a structural analysis of this region will correlate any repeats or structures with centromere function. This analysis will be performed using genetic techniques developed in yeast systems for analysis of more simple centromeres. Additionally, a molecular strategy will also be used toward this end. Finally, conserved components of centromere will be isolated for comparative study, and eventually for use to isolate more specific components of this centromere. This system may be the most advantageous for analysis of complex centromeres.